Verbalize your emotions, needs, preferences, and choices without aggression but with assertiveness and determination. Some abusers -- the narcissistic ones -- are detached from reality. They avoid it actively and live in fantasies of everlasting and unconditional love. They refuse to accept the inevitable consequences of their own actions. It is up to you to correct these cognitive and emotional deficits. You may encounter opposition -- even violence -- but, in the long-run, facing reality pays.
Play it fair. Make a list -- if need be, in writing -- of do's and don'ts. Create a "tariff" of sanctions and rewards. Let him know what actions of his -- or inaction on his part -- will trigger a dissolution of the relationship. Be unambiguous and unequivocal about it. And mean what you say. Again, showing up for counseling must be a cardinal condition.
Yet, even these simple, non-threatening initial steps are likely to provoke your abusive partner. Abusers are narcissistic and possessed of alloplastic defenses. More simply put, they feel superior, entitled, above any law and agreement, and innocent. Others -- usually the victims -- are to blame for the abusive conduct ("see what you made me do?").
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 2 DVDs with 12 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/thebook.html)